Method of making high voltage condensers



July 3, 1951 e. H. WILLIAMS METHOD OF MAKING HIGH VOLTAGE CONDENSERS Original Filed Dec. 28, 1943 8 R H mm N NL R m n mwgr a? M 7 W 6w Patented July 3, 1951 UNITED STATES PATENT FFICE METHOD OF MAKING HIGH VOLTAGE CONDENSERS of Delaware Original application December 28, 1943, Serial N 0.

1947, Serial No. 745,287

Claims.

This application is a division of my copending abandoned application, Serial No. 515,397, filed December 28, 1943. The parent application contains claims directed to the condenser, whereas this application contains claims directed to the method of testing and making the condenser.

This invention relates to a new and useful high voltage condenser of rugged construction.

An object of this invention is to simplify and improve high voltage condensers generally.

Another object of this invention is to provide an improved high Voltage condenser having a minimum number of parts, which condenser is therefore inexpensive to manufacture.

A feature of this invention is the simple arrangement of concentric electrodes which are molded within a block of plastic insulating material which completely envelops and supports the electrodes except for a small terminal portion at the ends of the condenser.

Briefly, the condenser of this invention is constructed by providing a combined mold and jig for supporting the electrodes which mold and jig also serves to determine the condenser capacity before pouring in the plastic material. Later the condenser is removed from the mold and machine finished in any desired manner, such as taking ofi any excess insulating material from the outer surface to present a smooth exterior.

The improved condenser of this invention and also the condenser of United States abandoned application Serial No. 515,343, filed by J. M. Morgan on December 23, 1943, are both used in a high voltage doubler circuit of a desk type electron microscope where the voltages are on the order of 20 to 30 kilovolts, although the condensers obviously have other valuable uses in circuits where extremely high voltages and rugged operating conditions are encountered.

This invention will best be understood by referring to the accompanying drawings, in which:

Fig. 1 is a cross-sectional view of the finished condenser;

Fig. 2 is a plan view of Fig. 1;

Fig. 3 is a cross-sectional view of the combined mold and assembly jig;

Fig. 4 is a plan view of Fig. 3; and

Fig. 5 is a partial sectional view taken on line 55 of Fig. 1.

Referring now in detail to Fig. 1 of the drawing, the finished condenser comprises a relatively heavy block I of insulating material which is preferably a plastic of polystyrene, or any other Suitable insulating material having the requisite Divided and this application May 1,

electrical insulating qualities. The outside surfaces are machine finished with rounded corners IA. A central electrode 2 supports a second or outer electrode 3, both electrodes being cylindrical in form. Electrode 3 may have located at one end thereof a plurality of small apertures 4 which permit bubbles to escape when the polystyrene is processed. The upper end of outer cylindrical electrode 3 is bent over at 5 to present a rounded surface for the prevention of corona. Located intermediate electrodes 2 and 3 is a third electrode 6 which is spaced equidistant between the metallic surfaces of the adjacent electrodes to provide a voltage breakdown on the order of 30 kilovolts. A tenminal stud l is secured to the closed end of electrode 6, the stud being fastened by means of rolling over a portion of the reduced diameter end as indicated at 5%. Electrode 5 is provided with a plurality of apertures 9 for the escape of bubbles as shown in Fig. 5 of the drawing. A terminal collar l G is fastened to the closed end of electrode 3 and is secured thereto by means of a stud II which also serves as a terminal for the condenser. Stud I l is provided with nuts [2 and washers l3. A threaded aperture 14 is provided for making connection to terminal stud 1.

Referring now in detail to Figs. 3 and 4 of the drawing, the condenser of this invention is manufactured within a combined mold and assembly jig which comprises a thin metallic mold 2|] having an aperture 2| located in the central portion at the bottom of the mold. An inwardly extending flange 22 is provided with apertures 23 through which pass fastening screws 24 for securing an insulating guide and assembly strip 25, such as a phenol condensation product, to mold 20. The stud II is supported within mold 28 by passing through an aperture 21 The terminal collar 10 is fastened on the inside of mold 211 by stud II. The outer electrode 3 is then fastened to stud II and is tightly secured thereto by means of the central electrode 2. Terminal stud 1, which has previously been secured to the intermediate electrode 6, is supported from an insulating strip 25 by means of an adjustable screw 26. A look nut 21 locks screw 26 in its desired position. A liquid seal washer 28 of any suitable gasket material is placed over aperture 2| and is secured in position by means of a nut 29 which is threaded on stud II for the purpose of forming a complete seal in the bottom of the mold 20. The condenser structure is connected in circuit with an electrical measuring device and then adjusted to its desired predetermined capacity value with air as a dielectric, taking into account the difference in dielectric constant of the insulating material- 2.358 in the case of polystyrene. For example, for a condenser having a finished capacity of 25 micromicrofarads, the screw 26 should be adjusted with the air dielectric until a capacity reading taken from the electrical measuring device, which device is connected between terminal stud H and screw 26 reads 10.26 micromicrofarads. After the condenser is adjusted for capacity, monomeric styrene is poured into the mold to a level indicated at 30, which is sufiicient to completely cover the entire condenser structure and to provide a finished condenser with a wall thickness which is substantially twice as large as the spacing between the intermediate electrode 6 and the electrodes 2 and 3. is then placed in an oven with a temperature of 132 degrees centigrade. A close check on the temperature should be kept at all times. The temperature of the styrene is never allowed to exceed 140 degrees centigrade or violent boiling will occur, filling the mass full of bubbles. Seventy-two hours at 132 degrees centigrade are required for the complete polymerization of the styrene. A suitable plasticizer may be added to the styrene to prevent cracking around the metal condenser electrodes. If it is desired to materially shorten the polymerization time, suitable accelerators can be used. The combined mold and assembly jig is then taken from the oven and the screws 24 and 26 are removed, thus permitting removal of the insulating strip 25. Washer 28 and nut 29 are removed from stud l I, and the sides of the mold 20 are then removed from the polystyrene block. The block is then placed in a lathe or other suitable machine and turned down to the desired outline, which is indicated by the dot and dash line 3|, which corresponds to the outline of the finished condenser structure as shown in Fig. 1.

If desired, a finishing or split mold, which approximately corresponds to outline 3|, may be provided, in which case it will be necessary to have the mold larger than the finished dimension to allow for shrinkage in process and in cooling.

While I have indicated and described a system of my invention, it will be apparent to one skilled in the art that my invention is by no means limited to the particular devices shown and described, but that many modifications may be made without departing from the scope of my invention.

What is claimed is:

1. A method of making a high voltage condenser of the type having an insulating exterior, including the steps of placing a plurality of elec trodes within a mold having an insulating support portion, joining terminal studs to said electrodes. connecting said studs to an electrical measuring device, adjusting the capacitance of said condenser to a predetermined value as in dicated by said device by moving one electrode in an axial direction in air with respect to said support portion to thereby adjust the capacitance of the condenser to a predetermined value different from but related to the desired capaci- The mold 4 I tance of the finished condenser, pouring insulating dielectric material into said mold, baking said dielectric material to harden the same, and thereafter removing said electrodes and insulating material from said mold.

2. A method in accordance with claim 1, wherein the insulating dielectric material poured into said mold is monomeric styrene and wherein the dielectric material is baked until the styrene is hardened by polymerization.

3. A method in accordance with claim 1, wherein the insulating dielectric material poured into said mold is monomeric styrene and wherein the dielectric material is baked at approximately C. for substantially 72 hours to harden the same.

4. The method of making an electrical condenser which includes placing a plurality of electrodes and terminal members arranged in an op posed position with respect to each other within a mold, said mold having metallic and insulating portions, one of said electrode and terminal members being secured to the metallic portion of said mold and another of such electrode and terminal members being secured to the insulating portion of said mold, electrically connecting the opposed terminal members to an electrical. measuring device, moving one of said electrodes and terminal members with respect to an opposed electrode and terminal member in air to thereby adjust the capacitance of the condenser to a predetermined value different from but rc-- lated to the desired capacitance of the finished condenser, pouring liquid, dielectric material into said mold to a predetermined level, placing said mold, dielectric material, and electrodes and terminal members within a heated oven, continuing the heating in said oven until the dielectric material is hardened, and thereafter removing the hardened condenser from said oven and removing said mold.

5. A method in accordance with claim 4, wherein the dielectric material poured into said mold is monomeric styrene and wherein the dielectric material is heated at approximately 130 C. for substantially 72 hours to harden the same by polymerization.

GURDON H. WILLIAMS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,351,787 Richter Sept. 7, 1920 1,558,043 Priess Oct. 20, 1925 1,650,395 Siegel Nov. 22, 1927 1,725,123 Bailey Aug. 20, 1929 1,837,142 Bailey Dec. 15, 1931 1,939,883 Edwards Dec. 19, 1933 2,291,445 Beyer July 28, 1942 FOREIGN PATENTS Number Country Date 515,891 Great Britain Dec. 18, 1939 

